1. Field of the Invention
The present invention relates to an optical switch and a using method therefor, and more particularly to an optical switch suitable for a node in a photonic network using wavelength division multiplexing (WDM).
2. Description of the Related Art
The development and commercialization of a wavelength division multiplexing (WDM) system are proceeding as a communication system that can greatly increase a transmission capacity. To construct a large-scale photonic network by connecting WDM systems, there has been examined a ring type or mesh type network obtained by connecting nodes through optical fibers in the form of a loop or mesh.
In the ring type network, a transmission capacity in the loop increases with an increase in scale of the network. However, in each node, it is sufficient to perform processing using a relatively small-scale optical switch. To the contrary, in the mesh type network, a transmission capacity in each-route is small, but it is necessary to perform processing using a large-scale optical switch in each node.
In a point-to-point link system, an electrical switch is conventionally used to extract lower-order signals in the node. By substituting an optical switch for the electrical switch, a cost in the node can be reduced.
Thus, the development of a large-scale optical switch is a key technology in constructing various types of networks.
A waveguide type optical switch is known as a conventional commercialized small-scale optical switch. The waveguide type optical switch includes a switch element and fiber arrays for inputs and outputs connected to the switch element.
For example, an optical switch referred to as a PILOSS type optical switch (Japanese Patent Laid-open No. 63-500140) has been developed to eliminate variations in loss according to the number of switch cells through which light is transmitted. This optical switch is configured by arranging N2 switch cells each having two inputs and two outputs at the lattice positions of a matrix with N rows and N columns and suitably connecting the inputs and the outputs of the switch cells so as not to cause the path dependence of loss.
As an optical switch which can enlarge an integration scale with a low loss, there has recently been developed a bubble type optical switch configured by forming a bulk at each crossover of crossing type optical waveguides and generating a bubble in the bulk to thereby obtain a total reflection condition. In each switch cell, the transmission and total reflection of light are switched to thereby obtain a switch function with two inputs and two outputs.
On the other hand, a configuration of spatially switching light is considered as a traditional technique. By using a reflection mirror as an element for changing an optical path, the problems in performance of the waveguide type optical switch, such as on/off ratio and crosstalk can be almost eliminated. However, such a space switch is large in volume, and it is therefore difficult to increase the scale of the switch from the viewpoint of size.
To break through such circumstances, there has recently been developed a technique of reducing the size of this space switch by using a semiconductor technology.
This technique is referred to as MEMS (Micro Electro Mechanical System), and it is also called optical MEMS in the case of application to the field of optics.
The optical switch using MEMS has a plurality of small mirrors formed on a substrate by a semiconductor fabrication technique, and performs switching of optical paths by selectively raising these mirrors by static electricity.
Information on MEMS may be provided by IEEE Photonic Technology Letters, Vol. 10, No. 4, APRIL 1998, pp. 525-527.
To increase the scale of a waveguide type optical switch, the yield of each switch cell itself formed on the switch element must be increased. However, increasing the yield is relatively difficult because of narrow manufacturing tolerances. Accordingly, in increasing the scale of the waveguide type optical switch, it is necessary not only to improve the yield by improving the manufacturing method, but also to remarkably improve the performance of the switch element.
In the bubble type optical switch, switching is performed by using the principle of total reflection in each switch cell. Accordingly, the angle of crossing of the two optical waveguides connecting the two inputs and the two outputs in each switch cell is as large as about 90xc2x0, causing an increase in switch size. In other words, if the bend radius of curvature of an optical waveguide connecting the adjacent switch cells arranged on the outermost side is reduced, the loss in this optical waveguide is increased. Therefore, the bend radius of curvature of this optical waveguide must be set to a sufficient amount. In connection with this setting, the pitch of the switch cells is determined, resulting in an increase in switch size.
In the waveguide type or bubble type optical switch, there is a case that crossover portions of the waveguides are required on the input and output sides, causing an unignorable loss.
Further, in the MEMS type optical switch, there is a possibility that the number of reflections on the mirrors may be different according to path in some mode of operation. Accordingly, in the case that the reflection loss by the mirrors is unignorable, there arises a problem that a path-dependent loss is produced according to a difference in number of reflections on the mirrors.
It is therefore an object of the present invention to provide an optical switch which can be reduced in size.
It is another object of the present invention to provide an optical switch which can eliminate the path dependence of loss.
It is a further object of the present invention to provide an optical switch which can suppress losses by eliminating crossovers of the optical waveguides.
Other objects of the present invention will become apparent from the following description.
In accordance with an aspect of the present invention, there is provided an optical switch comprising a plurality of switch cells arranged in the form of an n xc3x97n matrix (n is an integer), each of the plurality of switch cells having first and second input ends and first and second output ends; and 2(nxe2x88x921) reflection cells. The plurality of switch cells are selectively driven so that one of the first and second input ends of the switch cells in the first column is optically connected to one of the first and second output ends of the switch cells in the n-th column. (nxe2x88x921) ones of the 2(nxe2x88x921) reflection cells are arranged so as to optically connect the first output end of the switch cell in the first row, the i-th column (i is an integer satisfying 1xe2x89xa6ixe2x89xa6(nxe2x88x921)) to the first input end of the switch cell in the first row, the (i+1)-th column. The remaining (nxe2x88x921) reflection cells are arranged so as to optically connect the second output end of the switch cell in the n-th row, the j-th column (j is an integer satisfying 1xe2x89xa6jxe2x89xa6(nxe2x88x921)) to the second input end of the switch cell in the n-th row, the (j+1)-th column.
With this configuration, the plural reflection cells are provided at the specific positions with respect to the plural switch cells, so that it is possible to avoid a size enlargement due to an increase in bend radius of curvature as mentioned above and to thereby provide a compact optical switch.
In accordance with another aspect of the present invention, there is provided a using method for an optical switch having a plurality of switch cells arranged in the form of an nxc3x97n matrix (n is an integer), each of the plurality of switch cells having first and second input ends and first and second output ends; and
2(nxe2x88x921) reflection cells. The plurality of switch cells are selectively driven so that one of the first and second input ends of the switch cells in the first column is optically connected to one of the first and second output ends of the switch cells in the n-th column. (nxe2x88x921) ones of the 2(nxe2x88x921) reflection cells are arranged so as to optically connect the first output end of the switch cell in the first row, the i-th column (i is an integer satisfying 1xe2x89xa6ixe2x89xa6(nxe2x88x921)) to the first input end of the switch cell in the first row, the (i+1)-th column. The remaining (nxe2x88x921) reflection cells are arranged so as to optically connect the second output end of the switch cell in the n-th row, the j-th column (j is an integer satisfying 1xe2x89xa6jxe2x89xa6(nxe2x88x921)) to the second input end of the switch cell in the n-th row, the (j+1)-th column. In this method, only the switch cells relating to the switch cells in the odd-numbered rows, the first column and in the odd-numbered rows, the n-th column or only the switch cells relating to the switch cells in the even-numbered rows, the first column and in the even-numbered rows, the n-th column are used.
According to this method, the number of reflections in an optical path connecting an arbitrary one of the inputs and an arbitrary one of the outputs is always 2, and the optical path length of each optical path is constant irrespective of path, thereby eliminating the production of a path-dependent loss. Further, there are no crossovers at the inputs and the outputs, thereby eliminating an increase in excess loss.
In accordance with a further aspect of the present invention, there is provided an optical switch applicable to a first optical fiber transmission line unit and a second optical fiber transmission line unit. The optical switch comprises a plurality of switch cells arranged in the form of an nxc3x97n matrix (n is an integer), each of the plurality of switch cells having first and second input ends and first and second output ends; and 2(nxe2x88x921) reflection cells. The plurality of switch cells are selectively driven so that one of the first and second input ends of the switch cells in the first column is optically connected to one of the first and second output ends of the switch cells in the n-th column. (nxe2x88x921) ones. of the 2(nxe2x88x921) reflection cells are arranged so as to optically connect the first output end of the switch cell in the first row, the i-th column (i is an integer satisfying 1xe2x89xa6i xe2x89xa6(nxe2x88x921)) to the first input end of the switch cell in the first row, the (i+1)-th column. The remaining (nxe2x88x921) reflection cells are arranged so as to optically connect the second output end of the switch cell in the n-th row, the j-th column (j is an integer satisfying 1xe2x89xa6jxe2x89xa6(nxe2x88x921)) to the second input end of the switch cell in the n-th row, the (j+1)-th column. The second output end of the switch cell in the first row, the i-th column is optical connected to the first input end of the switch cell in the second row, the (i+1)-th column. The first output end of the switch cell in the n-th th row, the j-th column is optical connected to the second input end of the switch cell in the (nxe2x88x921)-th row, the (j+1)-th column. The first output end of the switch cell in the k-th row (k is an integer satisfying 2xe2x89xa6kxe2x89xa6(nxe2x88x921)), the i-th column is optically connected to the second input end of the switch cell in the (kxe2x88x921)-th row, the (i+1)-th column. The second output end of the switch cell in the k-th row, the i-th column is optically connected to the first input end of the switch cell in the (k+1)-th row, the (i+1)-th column. The first input ends of the switch cells in the odd-numbered rows, the first column and the second output ends of the switch cells in the odd-numbered rows, the n-th column are inserted in the first optical fiber transmission line unit. The second input ends of the switch cells in the even-numbered rows, the first column and the first output ends of the switch cells in the even-numbered rows, the n-th column are inserted in the second optical fiber transmission line unit.
With this configuration, the method according to the present invention is applicable to bidirectional transmission to thereby obtain an effect that the switch cells can be efficiently used in addition to the above-mentioned effect by the method according to the present invention.
In accordance with a still further aspect of the present invention, there is provided an optical switch with N inputs and N outputs (N is an integer). This optical switch comprises a plurality of switch cells arranged at the lattice positions of a matrix with n rows (n=2Nxe2x88x921) and (n+1) columns; and two mirrors arranged perpendicularly to a plane defining the matrix and parallel to each other so as to interpose the plurality of switch cells. The number and positions of the plurality of switch cells are set so that input paths corresponding to the N inputs and output paths corresponding to the N outputs are parallel to each other and that the number of reflections in an optical path connecting each input path and each output path becomes 2.
With this configuration, by arranging N2 switch cells at predetermined ones of the lattice positions of the matrix with n (n=2Nxe2x88x921) rows and (n+1) columns, the number of reflections in an optical path connecting an arbitrary one of the inputs and an arbitrary one of the outputs can be fixed to 2, thereby eliminating the path dependence of loss.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of reference to the attached drawings showing some preferred embodiments of the invention.